Electrical sorting system



June 6, 1961 Filed Jan. 23. 19

G. VAN MECHELEN 2,987,705

ELECTRICAL SORTING SYSTEM SORTED SORTED POSITION POSITION A H aCOMPARING COMPARING a SORTING & SORTING POSITION POSITION COMPARING aSORTING POINTS POSITION PRESORTING PRESORTING POSITION POSITION F/gi Hg.2. H9. 5'.

Inventor G. VAN MECHELEN By win;

Attorney June 6, 1961 G. VAN MECHELEN ELECTRICAL SORTING SYSTEM 5Sheets-Sheet 2 Filed Jan. 25, 1957 lnvenlor G. VAN MECHELEN A ttorn 2yJune 6, 1961 e. VAN MECHELEN 2,987,705

ELECTRICAL SORTING SYSTEM Filed Jan. 25. 1957 5 Sheets-Sheet 3 l -L5 PP3A G. VAN MEC HELEN y/Wm A ltorney June 6, 1961 G. VAN MECHELEN2,987,705

ELECTRICAL SORTING SYSTEM Filed Jan. 23. 1957 5 Sheets-Sheet 4 Woo us iE i i J L I m l i 5 i 0 j 0 1 l l I I 1 ri T1 h n n n TU/IS J k L L L J\L 59.4

inventor c5. VAN MECHELEN United States Patent 2,987,705 ELECTRICALSORTING SYSTEM Guillaume Van Mechelen, Antwerp, Belgium, assignor toInternational Standard Electric Corporation, New York, N.Y., acorporation of Delaware Filed Jan. 23, 1957, Ser. No. 635,884 Claimspriority, application Netherlands Jan. 31, 1956 4 Claims. (Cl. 340-1725)The invention relates to an electrical sorting system. Moreparticularly, it relates to an electrical sorting systern using theprinciple of sorting by collating.

The principle of sorting numbers by collating implies comparisonsbetween sets of numbers which are then made to form a sequence ofordered numbers. Such comparisons can be repeated until all numberswhich were initially in a random order are finally obtained in apredetermined order, i.e. a single sequence with all numbers increasingor decreasing in values starting from the first. It leads essentially toall numbers being classified in their natural order at the end of thesorting process.

If a sequence is defined as a series of numbers which are in theprescribed order, the sorting process will involve a gradual reductionof the number of sequences. The initial number of sequences may be equalto the total number of numbers to be sorted, if they happen to beinitially in the reverse order with respect to the predetermined orderdetermining the way of sorting. In that case, each initial sequencecomprises only a single numher.

What appears to be the simplest Way in which such comparisons can beconceived is to initially compare sets of two numbers and each timebuild a sequence of two numbers which are made to follow one another.When all numbers have been paired in this way, the new succession of allnumbers can at most include a number of sequences equal to about halfthe total number of numbers to be sorted. Then, a new sort can be madeto obtain sequences of four numbers and this time the new succession ofall numbers can at most include a number of sequences equal to about onequarter of the total number of numbers to be sorted. By continuing inthis manner, a single sequence, with all the numbers in the desiredorder, will finally be obtained.

The above principle of sorting is described in more detail by J. W.lviauchly in Lecture 22 entitled Sorting and collating" and part ofvolume III of Theory and Techniques for Design of Electronic DigitalComputers," Moore School of Electrical Engineering, University ofPennsylvania, June 30, 1948.

Such a principle of sorting by collating, which is binary in the sensethat two sequences of numbers are compared to one another, or ultimatelytwo numbers are compared to one another, has already led to practicalindustrial applications for automatically merging or interrneshing twoordered sequences of punched business cards into a single sequence. Suchmachines are well known and one may refer for example to the US. PatentNo. 2,597,647.

When such a principle is used to build a single sequence from aninitially arbitrary number of sequences, Le. a group of numbers with anarbitrary or random distribution, and by successive predetermined stepsas explained above, some ineificiency is noticed. Indeed, the system ofbinary collation explained above will require the complete file of Nnumbers to be processed log; N times, taking the next larger integralvalue of this expression, e.g. 7 times if N=:l00. But, considering theextreme cases precisely the same number of sorting passes will berequired if the N numbers happen to be initially arranged in exactly thedesired order, or in the order which is the exact reverse of the desiredone.

ICC

In the book by R. K. Richards entitled Arithmetical Operations inDigital Computers" on pages 296 to 299, a modified principle of sortingby collating is referred to, which has the advantage of using whateveraccidental classification is already present in the initial randomdistribution of the numbers or in any further intermediate distribution.

Just as the chances that the numbers are initially in the wanted orderare most remote, the same is true with respect to the numbers beinginitially in the order exactly opposite to the desired one. Hence, ingeneral the initial number of sequences will be appreciably smaller thanN, the total number of numbers. If from the first pass, one compares afirst sequence with a second sequence and the two which may both be ofarbitrary length are merged to form a single sequence, an existingsequence shall never be broken and a minimum number of sorting passeswill be used to obtain the final unique sequence in which all the Nnumbers are ordered as desired. Further, all sorting passes are alikeand it is no longer necessary to count sequences of 2, 4, 8, 16, etc.according to the pass considered.

The last principle explained above necessitates the use of two inputlists of numbers and two output lists of numbers. Initially, if it isassumed that the desired order is smaller in front and highest last, thefirst numbers from both input lists will be compared and the smaller ofthe two, C, will be placed as first number to start an output list.Next, the second number, A, from the input list which has supplied thefirst number, C, of the first output list will be compared with thefirst number, B, of the other input list as well as with the number C.If A and B are both larger or smaller than C, the smaller of A or B willbe placed as second number of the output list already started by C or asfirst number to start the other list respectively. If only A or B islarger than C, which is larger will be placed as second number of theoutput list already started by C. As A or B is placed in an output list,a new number from the input list having supplied A or B enters into thecomparison of three numbers which has just been explained. After all thenumbers have been sorted in that manner, the sorting pass is ended andthe two output lists can be considered as input lists for a furtherpass. Upon a single output list only being obtained, at the end of apass, the sorting process is ended, all numbers being in the desiredascending order.

The main object of the invention is to realize an electrical sortingsystem embodying the above principle in such a way as to produce asimple and reliable arrangement.

In accordance with the main characteristic of the invention, anelectrical sorting system wherein electrically represented numbers, e.g.cheque account numbers, eventually associated with electricallyrepresented satellite information, e.g. cheque amounts, and eventuallycorresponding to physical objects, e.g. cheques or cheque carriers, tobe sorted, are sorted by a binary collation process consisting inobtaining from a pair of initial successions of N and N numbers arrangedin any arbitrary order, a new pair of successions of the N +N numbers,in such a way that the first sequences of numbers ordered in the desiredway and found in said two initial successions are merged together toconstitute the first sequence of the first new succession, the secondsequences found in said two initial successions being merged together toconstitute the first sequence of the second new succession, and similarmerging operations producing a new sequence alternately for the firstand the second new successions, has the characteristic that twoelectrical shift registers are provided each with at least n+1 stageswhere n is the number of binary digits needed to characterize anynumber, that said two registers are respectively used to record a numberfrom the first and from the second initial succession, that as a newnumber A from one of said initial succession is progressively insertedinto one of said registers it is compared digit by digit with the numberC previously recorded in this one register and which is progressivelyturned out of said one register, that said new number A while beinginserted in said one register is simultaneously compared digit by digitwith the number B previously recorded in said other register and whichprogressively re-circulates through said other register, that after saidnew number A has taken the place of said number C while said number Bhas taken its initial position in said other register, the meansrecording the results of the comparisons indicate the order of A, B andC, whereby in accordance with said results, said recording means causethe next number from said first or second initial succession to beinserted in a similar manner into the register corresponding to saidfirst or second initial succession while the number which is thenremoved from said corresponding register is stored as the next number ofone of said new successions, also in accordance with said results.

The above mentioned and other objects and characteristics of theinvention will be better understood by referring to the followingdescription of a detailed embodiment of the invention in relation to theaccompanying drawings which represent:

, FIG. 1, a diagram explaining the operations at a sorting stage;

FIG. 2, electronic circuits for comparing the numbers inscribed on thedocuments to be sorted;

FIG. 3, electrical control circuits cooperating with those of FIG. 2 andshows control circuits using telephone type relays which are designed toactuate the mechanisms (not shown) of the sorting stage in accordancewith the result of the comparison performed by the circuits of FIG. 2;

FIG. 4, pulse waveforms appearing at various terminals;

FIG. 5. the comparator circuit represented as a block in FIG. 2;

FIG. 6, a comparator unit represented as a block in FIG. 5;

FIG. 7, the way to assemble FIGS. 2 and 3.

Referring to FIG. 1, it shows a diagram useful to explain the sortingprocess which the electrical circuits to be described later on are tocontrol. Seven positions have been shown on the figure. The first twopositions A and B are to indicate positions in which the first documentsout of two input stores of documents will arrive. When the firstdocument of the first input store is in the A position and when at thesame time the first document of the second input store is in the Bposition, sorting can proceed by dispatching either the document in theA position to the intermediate position A, or by dispatching thedocument in the B position to the inermediate B position. Betweenpositions A and A as well as between positions B and B, reading devices(not shown) will be assumed to be located in such positions that as thedocument moves along these respective positions, the characteristicnumber of the document which will determine how the document will besorted, will be automatically analysed and a record of this analysiswill be made.

When two documents have respectively reached the A and 13' intermediatepositions after having had their numbers read, electrical comparisoncircuits will be in a position to determine which document bears thesmallest number, or eventually if the two documents bear equal numbers.

If it is assumed that the sorting process is to be such that the finalsorting pass should produce all the documents with numbers in ascendingorder, the smallest numbered document being in front and the highestnumbered document being the last, the smaller numbered document in the Aor B position will be further displaced to reach the points position H,while the other document will remain in its intermediate B or Aposition.

At the same time that the two documents in the intermediate positionswere compared, a comparison should also have been made between thenumbers characterising these documents and the number of the documentwhich was the last to go through the points position H. In this mannerthree numbers are compared and considering the inequalities only, thereare therefore six possibilities:

For these conditions, A and B represent the numbers of the two documentswhich have been moved forward from the A and B positions respectively,while C represents the number of the document which was the last onehaving previously gone through the points position H.

The sorting by collating process which is to be controlled by theelectrical circuits to be described later, is based upon the idea ofbuilding sequences of numbers from two inputs of numbers which areinitially in any order whatever. It will be assumed that it is desiredto obtain a final sequence comprising all the numbers and in anascending order. The smallest sequence which can be present in the inputpiles of documents is the one comprising a single document only. This isthe case when that document is preceded by a higher numbered documentand followed by a lower numbered document. As the documents go through afirst stage of sorting, by comparing a document from one input with adocument from another input it will always be possible to build up asequence comprising these two documents, by simply forwarding the lowernumbered document in front of the other document. As long as it ispossible to forward a document which has a higher number than thepreviously forwarded document, that higher numbered document may followthe previous one in the same direction. When neither of the twodocuments accompanying the input positions are higher than thepreviously forwarded document, the previously built sequence must nowend and a new sequence should now be started by dispatching the lowernumbered document. It is however desirable to dispatch the firstdocument of this new sequence along another direction than the onepreviously used for the sequence which has just been terminated. In thismanner, one obtains two outputs of documents which can contain varioussequences, the number and the size of these sequences being arbitraryand depending on the original distribution of the documents.

The two outputs of documents which are thus obtained are convenientbecause they can then be used as respective inputs for a second sortingstage which, as well as the further stages, will sort in exactly thesame Way as the first sorting stage. The first output positions of therespective output stores have been indicated by C and D in FIG. 1.

Referring to the first of the six inequalities previously mentioned, Bdocument should follow the C document since this will not break thecurrent sequence and since this current sequence can in any case befurther increased in size by one unit by forwarding at least the Adocument after the B one.

Referring to the second inequality, the conditions are the same as forthe first one except that the order of A and B is now reversed whichmeans that the A document is the one which should follow the C document.

Referring to the third inequality, only the A document is greater thanthe C one and accordingly only that A document can be sent forward inthe same direction as C in order not to break the current sequence.

Referring to the fourth inequality, the conditions are the same as forthe third except that the order of A and B is reversed which means thatthe B document should now follow the trace of C.

Referring to the fifth inequality, neither A nor B is greater than C andaccordingly the current sequence must now be broken. The B document willbe the one to go forward but in the opposite direction to that followedby C in order to start a new sequence. It is the B document which issent forward because this leaves the possibility of building a newstquence containing at least two documents since A will be able tofollow B.

Referring to the sixth and last inequality, the conditions are the sameas for the fifth, except that the order between A and B has beenreversed which means that the A document will now be sent forward in theopposite direction to that followed by C.

When a document reaches the points position H, it can be assumed thatthe points will be automatically switched over in the one or the otheroff normal position so as to direct the document caried by the pointseither in the direction of the first output position C or of the firstoutput position D. As soon as the document leaves the points position Htowards either the C or D position, one can further assume that thepoints will be automatically restored to their normal condition ready toaccept the next document either from the intermediate position A or fromthe intermediate position B. As will be explained later, at this momentone should permit a new document to leave position A in order to reachposition A, or another document to leave position B to reach position B.Which document will be moved will of course depend on the origin of thedocument which was directed by the points. If that previous documentcame from the intermediate position A', the intermediate position B isstill occupied by a document and accordingly it is the next documentoccupying position A which should be moved to position A. In th: reversecase, it will be the document from position B which will be moved toposition B.

The electrical control circuits necessary to control a sorting stagefollowing the rules explained above, will now be described.

To fix ideas, it may be assured that the documents are cheques insertedor otherwise supported in an individual carrier per cheque. This has theadvantage of permitting the sorting of chequ es of varying sizes and toobtain standard dimensions and physical properties for the documents tobe sorted which facilitates the design of the sorting machine. Apartfrom bearing a cheque, the carrier will also bear a piece of magnetictape on which information pertaining to the cheque will have beenpreviously recorded. This information may b: though to consist of theaccount number of the cheque together with its amount. Thus, the amountis the satellite information previously mentioned. These two numbers maybe serially recorded on the piece of magnetic tape and the sorting willbe assumed to be made in accordance with the account numbers andsubsidiarily, for equal account numbers, in accordance with the amounts.

Initially, the two inputs of the sorting machine which is not shown herewill be filled by documents pressed against one another and for eachinput store, the first document of the stack will be in the positions Aand B (MG. 1) respectively. These two first documents are then ready topass through the first sorting stage of the machine which will providetwo new series of documents as these are progressively delivered to theoutput stores of which the first positions C and D have been shown. Itis not essential that there should be an equal number of documents ineach of the two input stores but for the first sorting stage of themachine, it appears nevertheless desirable that the documents should bemore or less evenly distributed between the two inputs. This will ingeneral give the best chances that ordered scquences of documents willbe merged together using as few sorting stages as possible.

It will be evident also that the control equipment to be described issuitable for one sorting stage of a sorting machine and that eachsorting stage of the machine will be provided with an entirely similarelectrical control equipment. The number of stages of the sortingmachine will best be determined by practical consideration such as thetime which can be allotted to the sorting of a certain number ofdocuments. In fact, the machine might well consist of one sorting stageonly which would be repeatedly used for several sorting passes, untilthe final sorting pass is made which will be characterised by the factthat all the documents after passing the points position H (FIG. 1) willalways be directed to the same output position such as C. At thismoment, the sorting process will be terminated and all the documentswill be classified in the desired order, i.e. the ascending order aspreviously assumed.

As each document passes from position A to position A or alternatively,from position B to position B, the piece of magnetic tape on which theaccount number of the cheque is recorded together with the amount, willbe read by a magnetic reading arrangement which will consist of twoheads. The first magnetic reading head will read a first magnetic trackon which synchronising information is inscribed by way of regularlyoccurring changes in the sense of magnetisation of the tape. The secondmagnetic reading head adjacent to the first will read a second track onthe magnetic tape which is parallel to the first and on whichinformation characterising the account number and the amount of thecheque is recorded, also by way of changes in the sense of magnetisationof the tape along this information track. As described in the US.application Ser. No. 411,523, filed February 17, 1954, a change in thesense of magnetisation on the information track can be taken torepresent one of the two binary digits, while the absence of such achange can be taken to represent the other of the two binary digits.This shows why the other track carrying the synchronisation informationis essential to be able to ascertain that for a particular unit bit ofmagnetic tape, there is a change in the sense of magnetisation for theinformation track or not. in this way, one determines the value of thebinary digit magnetically stored on that particular bit of tape.

The outputs of the two magnetic reading heads will be connected tosuitable amplifying and shaping devices, for example of the typedisclosed in the US. Patent No. 2,704,361.

FIG. 2 shows four terminals PA PB PA and PB, to which the pulses comingfrom the four reading heads located between positions A and A on the onehand, and positions B and B on the other hand are applied. At terminalPA regularly occurring clock pulses are obtained by reading the clocktrack of a document passing from position A to position A. At terminalPB corresponding clock pulses appear when a document passing fromposition B to position B is being read. At terminal PA eventualinformation pulses are read from the information track of a documentpassing from position A to position A. At terminal PR correspondingeventual information pulses appear as a document passing from position Bto position 8' is read.

For the information pulses, i.c. pulses FA and P13 it will be assumedthat a pulse appears to indicate the binary digit 1 while the absence ofa pulse indicates the binary digit 0.

FIG. 4 shows the type of pulse wave forms which may appear either at thepair of terminals PA and FA or at the pair of terminals PB and PB Asshown, the information pulses regularly recur with a period of 200microseconds, while the eventual information pulses characterising thebinary digit 1 are in anti-phase with respect to the information pulses.The partial information pattern shown in FIG. 4 therefore corresponds tol ll Since when a document passes from position A to position A in orderto replace the document previously located in position A, there is atthat time no document passing from position B to position B, this meansthat the two pairs of reading heads shall never be effective at the sametime and accordingly it is of interest to provide amplifying and shapingnetworks which can be used in common for the two reading positions. FIG.2 shows that terminal P and terminal P for reading the clock pulses onboth positions are both connected as inputs to the same mixer gate Gafter passing through the individual coincidence gates G and G Thesegates are indicated by circles and their input conductors terminate byarrows pointing towards the centre of the circle, while the numeralinside the latter indicates the number of input conductors which must besimultaneously activated in order to produce an output signal. Thus, theor, or mixer, or buffer gates such as G, show a 1 inside the circlewhile the and or coincidence gates with two input conductors show a 2 orhigher number inside the circle.

Hence, if gates G and G are never simultaneously unblocked, but only oneat a time, the mixer gate G may be assumed to contain the necessarycommon ampli fying and shaping means which will serve either for theclock pulses appearing at terminal P or those appearing at terminal P Ofcourse, the pulses appearing at these terminals may in fact have alreadybeen preamplified if necessary so that the gating action of G and Gtakes place at a suitable level.

In general, it should be remarked that the description will only beconcerned with the logical functions to be performed and that thedevices which are needed to amplify or shape signals will not beparticularly detailed. The designer should have no difiiculty inselecting the appropriate devices which may be necessary to obtainsuitable voltage current or power levels as well as suitable shapes forthe signals, and this in accordance with the elements and combinationsthereof which he wishes to use.

Gates G and G are respectively controlled by two of the comparatoroutputs. This comparator CP is merely represented as a block diagram inFIG. 2 but its details are shown in FIGS. 5 and 6 which will bedescribed later. The four outputs of the comparator CP are representedby terminals P P P and P Terminals P and P are used to produce signalswhich will determine which document is to be advanced towards one of theoutput positions C or D (FIG. 1). Either an activating signal willappear at terminal P to indicate that a new document should be advancedfrom the input. position A, or it will appear at terminal P to indicatethat a new document should be advanced from the input position B (FIG.1). Since terminal P is connected to G while terminal P is connected toG either G or G will be able to pass the clock signals from terminals Por P These clock signals appearing at the output of G when a document isbeing read either between the positions A and A or between the positionsB and B, will be applied to the input of a monostable device MS,represented by a rectangle divided into two squares each indicating thetwo possible conditions of the device. Condition 0 is the normal stablecondition, while the indication of 3G microseconds inscribed in thesecond square indicates the time constant of M8 i.e. the time it takesto return to its stable condition after having been triggered to itsunstable condition. Hence, at the output of MS; pulses corresponding tothe received clock pulses will be applied to the mixer gate 6;, butthese pulses have a relatively well defined duration of 30 microsecondsand the same period as the clock pulses, i.e. 200 microseconds. Thewaveform of these pulses is shown in FIG. 4.

From the output of G the received pulses are used as advancing pulsesfor the two shift registers SRA and SRB. Each of these shift registersis represented by a rectangle divided into n+2 squares, the first andthe last squares respectively marked by 0 and n+1 being separately shownfrom the others. Each of these squares represents a stage of the shiftregister which may for example be designed in accordance with the US.Patent No. 2,649,- 502. Each square representing a stage of the shiftregister can occupy two possible electrical conditions and accordinglythe shift register can be used to record a number electricallyrepresented by n binary digits plus an additional binary digit. Theadditional stage labelled O and which is separated from the next stagesby the gates such as G and G has been found convenient as an input stagein order to permit the advancing pulses to lag with respect to theeventual information pulses. This may be useful when possibleundesirable phase shifts between the clock pulses and the eventualinformation pulses can occur due to inaccuracies produced by the readingdevices. As shown, the advancing pulses issued from the output of G areapplied to all the stages of SRA and SRB. Each advancing pulse willcause the digital pattern registered on SRA and SRB to be advanced byone stage. As disclosed in the US. Patent No. 2,649,502, each stage mayessentially include a cold cathode tube which may be ionized or not, andthe advancing pulses will be applied to the cathodes of all the tubes insuch a way as to de-ionize all the previously ionized tubes and leavethe non-active tubes tie-ionized. Upon the disappearance of theadvancing pulse, thus after some 30 microseconds, those tubes which hadpreviously been ionized will still provide a transient pulse in theiranode circuit which will be sufficient to cause the ionization of thenext tube forming the next stage, a suitable coupling between the anodecircuit of any tube and the control circuit of the next tube beingprovided.

Just as the clock pulses appear either at terminal P or at terminal Pthe eventual information pulses corresponding to these clock pulses willappear either at terminal P or at terminal P depending on whether adocument is passing from position A to position A, or from position B toposition B. These information pulses are applied to inputs of the gatesG and G through a gating arrangement comprising the coincidence gates Gand G as Well as the mixer gate G The gating arrangement comprising 6 Gand G will be recognized as exactly similar to the gating arrangementcomprising G G and G Again, the activating condition present either atterminal P or at terminal P will unblock the A or the B path by way ofunblocking G or G respectively.

The gates G and G; are essentially information entrance gates to SRA andSRB respectively. These coincidence gates are controlled from terminalsP and P respectively. They are further controlled from the terminal P atwhich a pulse condition will appear during part of the time taken by thedocument to pass from the position such as A to the correspondingintermediate position A. With a view to provide a pulse of suitableduration and position at terminal P one may consider that this isproduced by a photocell arrangement comprising at least two cells. Thesetwo photocells which are not shown, may be assumed to lie in series inthe path between A and A. When the passage of the document blocks thefirst photocell which it meets during its travel towards its position A,this will correspond to the leading edge of the pulse to be produced atterminal P One will arrange that at that moment, the piece of magnetictape bear- 9 ing the information is already engaged under thecorresponding reading heads but that the surface of the tape printedwith the account number of the cheque and followed by the amount of thelatter has not yet been reached. When the front edge of the documentmoving towards position A now blocks the second photocell, this willcause the termination of the activating pulse condition at terminal PThis second photocell will be located in such a position that thistermination of the activating pulse at this terminal will happen whenthe piece of magnetic tape is still travelling under the correspondingreading heads, but when the area printed with the information hasalready filed past these heads. Hence, the purpose of this authorizingpulse at terminal P is essentially to permit inserting the informationprinted on the magnetic tape only when it is really there, in order toavoid noise or other spurious signals picked up by the reading headsbefore or after the actual information is read, to be sent towards SRAor SRB. At terminal P will also appear a corresponding authorizing pulsewhen a document is passed from position B to position B, thisauthorizing pulse being generated by an exactly similar photocellarrangement located this time on the path of a document moving betweenpositions B and B.

From what has been described so far, when a document is being read, theclock pulses at the output of G; will always produce advancing pulses atthe output of G which will be used to advance the information patternboth on SRA and on SRB, irrespective of whether the document which isbeing read is an A or a B document. At the same time however, theinformation pulses will either be able to flow through G or through Gdepending on whether an A or a B document is being read.

If it is assumed that a clock pulse or an advancing pulse always followsthe eventual information pulse, and if it is assumed that patterns of nbinary digits are already registered on stage 1 to n of SRA and of SRB,the first advancing pulse will advance these two patterns by one stageso that they will occupy the stages from 2 to n+1 in SRA and SRB.Immediately before this first advancing pulse however, the presence orthe absence of an information pulse on the A document, will have causedstage of SRA only to be placed in a condition corresponding to the firstbinary digit. If a pulse appears at the output of G one will assume thatthe 0 stage of SRA will record a 1, while it will be assumed to record a0 if there is no such pulse.

Further advancing pulses will continue to advance the patterns on SRAand on SRB, but as the pattern on SRA is advanced, a new informationpattern is gradually inscribed and represents the new information whichis being read from the document travelling between positions A and A.Whereas the previous information pattern registered on SRA is beinggradually pushed out from this shift register and lost, as the binarydigits gradually go out from the last stage n+1, this is not the casefor the previous information pattern registered on SRB. For the latter,since it has been assumed that terminal P is activated, the signal atthis terminal will permit to unblock the coincidence gate G which isinserted in the ring coupling between stage n and stage 1 of SRB. Thisgate G is also controlled by the bistable device BS1 which, as will bedescribed later, should be assumed to have been placed in its condition1 at the start of the operations. Hence, when terminal P provides anactivating signal, gate G is unblocked and as the previous pattern ofinformation is advanced through SRB it is gradually reinscribed throughgates G and G in series.

An identical ring coupling including the coincidence gate G and themixer gate 6,; is provided between stages n and l of SRA but thiscoincidence gate 6,; is controlled by the activating condition which maybe present at terminal P which has been assumed to be inactive for theexample considered.

When the first digit of the pattern previously registered 10 i 1 on SRAcomes into stage n+1, the first digit of the information being read fromthe A document travelling between positions A and A will occupy stage 1of SRA. At the same time, the first digit of the pattern previouslyregistered on SRB will occupy stage n+1 of SRB, as well as stage 1 ofSRB since this previous information pattern is able to recirculatethrough G Stages 1 of SRA and SRB are respectively coupled to theterminals P and P of the comparator CP. Also, stages n+1 of SRA and SRBare respectively coupled to the terminals P and P of this comparator CP.

This comparator CP which is detailed in FIGS. 5 and 6 is arranged sothat it can always compare the pairs of conditions which successivelyappear at terminals P and P It can also compare the pairs of conditionsat terminals P and P Further, it can compare the pairs of conditionsexisting at terminals P and P In this manner, while a new number A isinserted into SRA to replace an outgoing number C previously stored inSRA and while a previously stored number B recirculates in SRB,comparisons between A and B, A and C, and B and B will always be made.On the other hand, while a new number B is inserted in SRB to replace anoutgoing number C previously stored in SRB. and while a previouslystored number A recirculates in SRA, comparisons between B and A, B andC, and A and A will always be made.

It is readily remarked that out of these three comparisons, one isalways pointless since it merely compares the previously stored numberwith itself. This particular comparison could therefore only be used asa check that things are proceeding in the right manner. But, the othertwo comparisons do not apparently permit the comparator CF to determinethe order of the three numbers, since in one case the order of B and Cis not determined and in the other case, the order of A and C is notdetermined. However, as will be explained later in relation to FIG. 5,the comparator CP is arranged in such a way that the two usefulcomparisons will nevertheless be sufficient to determine the order ofthe three numbers A, B and C and accordingly to activate either terminalP or terminal P to cause one of the two documents A and B to moveforward to the points position H (FIG. 1) in accordance with the resultof the comparisons. Also, the comparator CP will produce an activatingsignal either at terminal P or at terminal P to give an indication tothe control circuit of FIG. 3 as to the output C or D (FIG. 1) to whichthe outgoing document should be sent. Hence there are four possibleresults of the comparisons performed by CP.

FIG. 2 also shows that the clock pulses applied to MS are directed toterminal P of the comparator CP. These pulses will be used in a mannerlater to be described, to activate the comparisons performed by thecomparator. Further, terminal P at which the authorising pulsesgenerated by the photocell arrangements appear. is also con nected toterminal P of the comparator CP. A condenser coupling issued to indicatedifferentiation of the authorising pulse and its leading edge will beused for resetting operations while its trailing edge will be used tofinally produce the activating signals at one of the two terminals P andP and at one of the two terminals P Ur PD.

At terminal P pulses having a duration of 30 microseconds and with aperiod equal to 200 microseconds appear. These pulses will thus beidentical to the pulses produced by M8 in response to the reading ofclock pulses, but the pulses at terminal P are locally generated andconstantly present at the input of the coincidence gate G At the startof a sorting pass, BS will be triggered to its 0 condition for a shorttime during which a sulficient number of the locally generated advancing pulses at terminal P will be able to flow through the gates Gand G in series in order to advance any residual pattern stored on SRAand SRB, or any pattern:

11 haphazardly set on these upon power being applied. The purpose ofthis operation is therefore to empty SRA and SRB so that when newsorting operations are started all the stages of SRA and SRB are intheir conditions corresponding therefore to the recording of 0 numbers.

It is desirable that at the beginning of the sorting op erattons 0numbers should be recorded in SRA and SRB since otherwise, the firstnumber A for example to be stored in SRA might be found to have such arelation to the initial arbitrary numbers stored in SRA and SRB, that itwould result in the corresponding A document being sent forward. Thiswould mean that the next A document would be recorded in SRA and thiswould not give an opportunity to the first B document, which has not yetbeen read, to be sent through the points position H (Fig. 1) immediatelyafter the first A document was sent forward.

Finally, the comparator CP also shows three additional input terminals PP and P to which signals may eventually be applied from the sequencecontrol circuit of FIG. 3 for a purpose which will be described later.

A description will now be given of the various sequences of operationswhich take place when a sorting pass is to begin. Before detailing theoperations which take place in the circuit of FIG. 3, a summary of thefunctions of the various key contacts represented and of the variousrelays will be given.

Contacts functions:

ks-start key contact.

kt--stop key contact (used to stop a sorting pass at any moment for thepurpose of restarting a fresh sorting pass).

ku lku -intermediate stop key contacts (to be used for the purpose oftemporarily stopping a sorting pass to be restarted later).

kv-batch sorting key contact (to be used when it is desired that uponone of the two input stores having sent all its documents forward, thedocuments remaining in the other input store are sent forward to one orthe other output positions in accordance with their initial sequences.Otherwise, flow sorting takes place which means that upon all thedocuments having left one input store, the sorting pass is stopped untilthis input store is refilled).

ka /kb -A and B input stores respectively occupied by at least onedocument in the corresponding input position.

ka /kb A' and B intermediate positions respectively occupied by adocument.

ka /k,b -points position H contacts indicating when they are bothoperated, that a document occupies the points position.

oj-points position H contact to indicate that the latter are in an offnormal condition.

Relays functions:

Ar/Br-lnitial indication that the next A or B document is to be advancedfrom the input position to the intermediate position and through thereading position, and to replace the corresponding document going in oneof the output stores.

Aar/BarDocument in the intermediate position to be advanced to thepoints position.

Abr/Bbr-Prepares, the advancement of a document from the input positionto the intermediate position.

Acr/Bcr-Advances, the next document from the input position to theintermediate position.

Adr/Bdr-Corresponding input store emptied of all its documents and tocause sorting to contlnue with the other documents in the other store inthe case of batch sorting.

Cr/Dr--Document in the points position to be directed to the C or to theD output position.

ErResponds to an intermediate or a final stop.

Fr-Releases Adr and Bdr upon both input positions having been emptiedafter batch sorting.

HarPoints occupation relay.

Hbr-Points liberation relay.

Hcr/Hdr-Occupied points to direct the document to the C or the D outputpositions.

Sr-Start relay immediately effective to cause the advancement of eitherthe first A or B document towards its intermediate position.

Sar-First start helping relay.

Sbr- Second start helping relay.

Scr--Start relay for advancing the first document from the other inputposition to the corresponding intermediate position.

Tr-Stop relay.

Ur-Intermediate stop relay.

Assuming that both input stores positions have been filled by a numberof documents to be subjected to a sorting pass, and that the inputpositions A and B are occupied by the first documents, the starting key,which may be a push button, will be temporarily depressed causing thetemporary closure of contact ks. Via break contact t of the stop relayTr which should not be operated at that moment, a circuit will beestablished between ground and a suitable battery potential at terminalP and this will energise the start relay Sr. Contact s therefore closesto provide a locking circuit for Sr independently of contact ks, andthrough the closed contacts aa and ba in series. The operation of Sralso displaces the change over contact s which interrupts the connectionbetween a suitable fixed D.C. potential at terminal P and the 0 input ofBS (FIG. 2). This will have the result of placing BS; in its 0 conditionif it was not already in that condition. This may, for example, takeplace in practice by causing the grid of one of the tubes forming theflip-flop BS to have its potential increased due to the opening producedby the operation of s; upon Sr being operated. This might cause anincrease of the resistance between this grid and ground, this grid beingon the other hand connected to the H.T. supply for the tube through theanode of the other tube forming the flip-flop and thus in conventionalmanner. If the tube, whose grid potential was so modified was notalready conductive, its plate-cathode space will now be ionized whilethe other tube will become non-conductive. Hence, from the operation ofcontact s the local advance impulses at terminal P will start to wipeout whatever information was contained in SRA and SRB (FIG. 2).

The operation of Sr will also produce the energisation of either relayAar through make contact 5 or relay Bar through make contact s Which ofthese two relays will be operated depends upon the initial condition ofthe comparator CP (FIG. 2). It is immaterial, at the start of theoperations, which of the terminals P or P and P or P are activated. Onemay assume for example that terminal P is activated while terminal P isnot. This will mean that, a suitable fixed DC. potential being presentat terminal P sutficient current will fiow between this terminal andterminal P (FIG. 2) so that relay Ar is initially energised while relayBr is not. Hence, relay Aar operates in a circuit including resistanceRa, contact s winding of Aar, contacts ac a and e The operation of relayAar will control a mechanism (not shown) which is able to displace adocument in the A intermediate position (FIG. 1) towards the pointsposition H. As no such document has yet reached any of the intermediatepositions, this first operation will be without any effect.

When relay Aar operates, through make contact aa and the winding ofrelay Abr, a locking circuit is closed for Aar independently of contacts The resistance Ra will be assumed to have a sufficiently low valuewith respect to the resistance of relay Abr so that this last relaycannot yet operate at this moment due to the short-circuiting effectproduced by resistance Ra. The operation of Aar also closes contacts mand aa Depending on which of the two terminals P or P happens to beactivated by the comparator CP (FIG. 2), either relay Cr or relay Drwill operate. One may assume, for example, that suflicient current flowsbetween terminals P and P so that through make contact aa relay Croperates. Then, relay Cr locks through its contact 0 in series withcontacts hb and SC; to ground.

When contact .53 closed, it establishes an operating circuit for relaySar which energises and locks through its make contact sa; in serieswith the break contact sc Upon relay Aar having been operated, contactaa opens to cause the release of relay Sr.

The release of relay Sr opens contact .9 whereby resistance Ra no longershort-circuits the winding or relay Abr which is now able to operate inseries with relay Aar through the series contacts aa ac a and e;.Contact ab closes whereby relay Aar is now short-circuited and releases,opening its contact aa but relay Abr remains held through its makecontact ab The release of relay Sr will also return contact .9 to theposition shown whereby the connection between the potential at terminalP and the 1 input of BS (FIG. 2) will be interrupted. As previouslyexplained in connection with the interruption, also by contact s of theconnection between this terminal and the 0 input of B5 this action willnow have the effect of placing BS into its 1 condition. From then on,recirculation of information will be permitted either for SRA or SRB,and for the latter in the case assumed here, since terminal P isactivated. Relay Sr has been indicated to be a slow release relay sinceit should stay operated for a time sufiiciently long to permit acomplete wiping out of the patterns which may be initially recorded onSRA and SRB. This time evidently depends on n and on the period ofadvancement of the patterns, and the slow release relay may eventuallybe associated with such known means which will permit to secure therequired time. Upon re lay Aar having been released while relay Abrremained held, an operating circuit is closed for relay Acr throughbreak contact aa make contact ab the winding of Acr and break contact eRelay Acr energises and will cause the first document in the A inputposition to be moved towards the intermediate position A. On its way toposition A, the first A document will be read as previously explainedand the number of the document which is read will be compared to thenumbers stored in SRA (FIG. 2) and in SRB. Since SRA and SRB are nowwiped out to record 0 numbers, the first A document will be foundgreater than the numbers of the non-existing documents. This means thatthe first A document should not be the one to be sent to the pointsposition H in accordance with the rules explained above, but that it isthe missing document corresponding to the 0 inscription in SRB whichshould be sent forward.

In the meantime, as soon as relay Acr operated to dispatch the first Adocument through the reading position and to the intermediate positionA, a circuit will have been established for the operation of relay Slirthrough make contact sa and make contact rin In operating, relay Sbrlocks through make contact sb and the winding of relay Scr independentlyof the contact n0 As long as this contact remains closed however, relaySrr remains short-circuited and cannot operate. The operation of therelay Acr will also open contact 00 thereby interrupting the holdingcircuit for relay Abr which releases. In turn, the release of relay Abropens the contact ab and relay Acr releases whereby relay Scr is pcrmitted to operate in series with relay Sbr.

In order to positively prevent that upon Scr being operated on therelease of relay Aer, Aar could be operated if relay Ar had not alreadyde-energised, a holding circuit is provided for relay Acr. This includesmake contacts ac a and sb in series. Hence, as long as Ar is still Crare now open.

operated, relaw Acr cannot be released. When the latter relay releases,the comparison circuit has reacted in a manner which is in factpredetermined and relay Aar cannot operate upon the operation of Scr.

By the time that the first document has reached the intermediateposition A, a renewed operation of relay Aar is prevented because theeventual operating circuit for this relay is opened at contact ac andalso at contact a since due to the comparison mentioned above, theactivating potential at terminal P (FIG. 2) will have disappeared to bereplaced by an activating potential at terminal P causing the operationof relay Br.

Hence, when relay Scr operates, contacts sc and so, will be closed, butwhereas the closure of contact s0 cannot cause the operation of relayAar, the closure of contact s0 will now establish an operating circuitfor relay Bar. This includes the resistance Rb. make contact s0 windingof Bar, contact be make contact and break contact e As previouslydescribed for relay Aar, relay Bar locks through contact ba in serieswith the winding of relay Bbr which cannot operate as long as it isshortcircuited by the resistance Rb.

When operating, relay Scr opens contact sq to interrupt the holdingcircuit for relay Sar which releases causing in turn the release ofrelays Sbr and Scr. Hence, the four starting relays Sr, Sar, Sbr and Scrare now released having performed their required functions.

The operation of relay Br will cause the corresponding mechanism toadvance a document in the B intermediate position to the points positionH. However, this will still be without effect since the B document ismissing. Upon the release of relay Scr, relay Bbr will be able tooperate as it is no longer short-circuited by the resistance Rb. Aholding circuit is closed for this relay through make contact bb andthis short-circuits relay Bar which releases. At this moment, a circuitfor the operation of relay Bcr is established through [m in series withbbg. The operation of relay Bcr will then cause the first document inthe B input position to be advanced to the B intermediate positionpassing through the corresponding reading position.

When relay Scr was operated, the opening of contact s0 interrupted theholding circuit for relay Cr which released. This means that thecontacts 0 and of relay Accordingly, although the first A document andthe first B document are now in their respective positions and thatconsequently the respective busy intermediate position contacts [m andkb are closed, neither the relay Anr nor the relay Bar can beshort-circuited through their own break contacts an or ha since bothrelays Cr and Dr are released.

Depending upon which of the first two documents A and B is the smaller,the comparison circuit CP will cause that document to be sent forward tothe points position. It will therefore be the first to pass through thispoints position.

If it is assumed that the A document is smaller, terminal P will havebeen activated when the first B document went through the correspondingreading position and accordingly relay Ar is operated permitting theenergisation of relay Aar. This time the operating circuit will includecontact ka instead of the contacts of the starting relays such as Sr orSer. In a manner entirely similar to that previously described, theoperation of relay Aar will cause the first document to be sent to thepoints position, but this time the operation of relay Abr will be due tothe fact that the first A document has left the intermediate position A,thereby opening contact k02- Upon the operation of relay Am, rclay Crwill reoperate through make contact aa since terminal P will still beactivated as there has not yet been any possibility for the outputposition to which a document should be directed to be changed. After therelease of relay Aar caused by the operation of relay Abr, relay Cr willremain locked through contact c hb and s0 Relay Acr will again operate,to cause the second A document to be moved from the input position andto take the place of the first A document which has left theintermediate position A to be dispatched to the points position H. Inturn, relay Abr releases and this causes the release of relay Acr sincethe latter is no longer provided with a holding circuit, relay Sbr beingreleased. The time of operation of relay Acr, just as that of relay Aarshould, of course, be assumed to be sufficient to cause the document tobe started either towards the intermediate position or towards thepoints position. Once the document has been started on its way, it isassumed that the mechanism will continue to propel it until it reachesthe desired position.

When the second A document moves through the corresponding readingposition, this might result in the comparator CP indicating that thefirst B document should now be moved towards the points position. Thiswould be the case for example if that first B document is greater thanthe first A document but smaller than the second A document. Hence,terminal P could be activated thereby causing the operation of relay Brinstead of relay Ar. When contact b closes however, since relay Cr isoperated, relay Bar is short-circuited by the series contacts kb 50 haand Therefore, relay Bar cannot yet operate at that moment. The reasonfor this is to prevent a document to be sent from one of theintermediate positions to the points position, when the latter mightstill be occupied by the previous document. A similar short-circuitingcircuit is provided for relay Aar (ka sc (m and 0 d When the first Adocument reaches the points position H (FIG. l), this will be assumed toproduce the closure of the two points contacts [m and M2,, upon thedocument having been fully inserted on the points position. If, as showndiagrammatically on FIG. 1, the sorting machine has two intermediatepositions A and B symmetrically located with respect to the pointsposition H, contact ka might be closed upon an A document entering thepoints position, while contact kb will be closed upon a documententering from the intermediate B position. However, it can be arrangedthat upon the document having been fully inserted in the points positionH while coming from the intermediate position A, contact kb will alsoclose following the closure of contact ka- (reversed sequence for a Bdocument entering the B points position).

Upon the closure of these two contacts by the first A document, relayHar operates and locks through its make contact ha; in series with thewinding of relay Hbr and contact c Relay Hbr cannot operate in thiscircuit as it is short-circuited by the series contacts ka and kb Theoperation of relay Har also results in Her being energised through makecontacts ha hbr and a in series. Relay Hcr will be assumed to be therelay responsible for displacing the points position containing thefirst A document in such a way that it is directed towards the outputposition C. Relay Hdr would, of course, have operated to direct the busypoints towards the output position D it relay Dr had been operated. Uponthe busy points position being displaced, the off normal contact of willprovide an additional locking circuit for relay Har.

The points will be assumed to be self controlled in the sense that uponthe busy points having been displaced to one of their two off-normalconditions, the document present on the points will be automaticallydispatched to the corresponding output position. When the documentleaves the points position, it will be further assumed that means notshown will cause the automatic return of the points to their normalposition ready to accept another document from either of theintermediate positions. Contacts kb;, and lea will be successivelyopened as the first A document leaves the point, but at that momentrelay Hbr is still short-circuited by otf normal contact of." When thepoints swing back to their normal position, contact of will be alsoopened and accordingly relay Hbr will operate in series with relay Har.The operation of relay Hbr opens at contact hb; the holding circuit forrelay Cr which releases thereby releasing relays Har and Hbr due to theopening of contact 0 At contact M the temporary operation of relay Hbrimmediately causes the release of relay Hcr.

Upon relay Cr having been released, contacts c and c are opened andeither relay Aar or relay Bar can be operated through their respectiveintermediate position busy contacts ka; or kb depending upon the resultsof the comparison. Whether Aar operates due to Ar being energised orwhether relay Bar operates due to relay Br being energised, will resultin operations similar to those already described. Likewise, upon theoperation of Aar, or Bar, either relay Cr or relay Dr will operate.Since the first A document was sent to the C output position, it isclear that relay Dr can only operate due to the activation of terminal Pupon both the first B document and the second A document having beenfound smaller than the first A document, which is the conditionindicating a change of output.

Sorting will continue in the manner explained, until the last documentfrom one of the two input stores has moved to the correspondingintermediate position. This document will remain in that intermediateposition in accordance with the control given by the comparison circuitCP, and during the time that A documents can still be sent through thepoints without necessitating the insertion of that last B document in anoutput sequence. Upon this last B document being sent to the pointsposition, it will not be replaced by a further B document in thatposition. Hence, no further information will be sent to the comparisoncircuit CP which will remain in the condition which caused the last Bdocument to be dispatched to the points position. Therefore, the sortingoperation will be stopped at that moment leaving an A document in thecorresponding intermediate position and eventually leaving furtherdocuments in the A input store.

This type of sorting operation may be termed flow sorting. The machinestops of its own upon one of the input positions having been emptied. Itwill be necessary to refill that input position in order to continue thesorting process. If the sorting stage considered is not the first inputsorting stage, one can wait until the previous sorting stage deliversfurther documents to the input store which has become empty at thesorting stage considered. By a further temporary closure of contact ks,a new start can be given and the sorting can continue. Of course, thismight be made automatic by providing a contact arrangement detectingthat documents are present in both input stores, which detection wouldhave a result analogous to the closure of contact ks.

In opposition to flow sorting, one can also consider what may be termedas batch sorting and which consists in completing the sorting operationsat any stage as long as there remain documents in one of the two inputstores, and despite the fact that the other input store has beenemptied. In that case, of course, the documents remaining in one inputstore will be merely sent forward in their present sequences. However,depending on these input sequences, these documents will bealternatively sent to the one and the other of the two output stores andthe next sorting stage will generally be fed at its two input stores.Therefore, with the batch sorting method, a sorting stage might have oneof its two input stores temporarily emptied but later refilled bydocuments coming through the previous sorting stage.

If batch sorting is desired, contact kv will be permanently closed bymeans of an appropriate key. Assuming that after a certain time, the Binput store is emptied and not immediately refilled by the next Bdocument, contact irb normally operated by the first document to go outof the B input store will be released when the last B document moves tothe intermediate position and is not replaced by a further B document inthe B input store. Upon relay Bar being operated when the last Bdocument in the B intermediate position is required to be moved to thepoints position H, an operating circuit for relay Bdr will be closedthrough break contacts 1 kb make contact ba the winding of Bdr, and makecontact kv and break contact e Relay Bdr operates and looks through makecontact bd; in series with break contact f After relay Bbr operates inthe normal manner causing the release of relay Bar and hence theoperation of relay Bcr, the latter will be without efiect since thereare no further documents in the B input position. The energisation ofrelay Bcr will cause the release of relay Bbr, in turn producing therelease of relay Bcr.

Upon relay Bdr being energised, change over contact bd is displaced andthe connection between terminals P (FIG. 3) and P (FIG. 2) isinterrupted. As will be shown later, this interruption, as long as itlasts, will have the result of forcing the comparator circuit CP whichhas hitherto remained in the condition previously attained and whichcaused the departure of the last B document to the points position, insuch a position that it indicates B C. Further, upon change over contactbd establishing a connection between terminals P (FIG. 3) and P (FIG. 2)a pulse will be applied to the comparator circuit CP for the purpose ofcausing an eventual reversal of output for the next A document to besent to the points position, and in a manner which will be detailedlater.

A further result of the operation of relay Bdr is the closure of makecontact bd which bypasses contact al so that irrespective of theoperation of relay Ar or Br, an operating circuit will always beestablished for relay Aar upon the closure of contact ka which will beremembered to be the busy contact for the intermediate A position. Onthe oher hand, relay Bar can never be reoperated from the moment thatthe last B document has left the intermediate B' position, since thebusy contact kbg will never be reoperated.

The reasons for the actions mentioned above and caused by the operationof relay Bdr can be explained as follows:

When the last B document was sent to the sorting position H, this mustmean that the comparator indicated A B C or its two cyclic derivations,i.e.

1 representing the number of the last B document, A that of the firstremaining A document, and C the number of the document which immediatelypreceded B through the points position H. Since no further 8 documentwas moved through the corresponding reading position, the comparatorcircuit shall normally not be affected and would remain in a conditioncorresponding to one of the three relations mentioned immediately above.Therefore, it is clear that the comparator still indicates that a Bdocument should be sent to the points position. Since this is pointless,the closure of make contact bd appears to give a correct remedy sincethis will permit the first remaining A document to be sent to the pointsposition upon the latter having been freed from the last B document, andthis independently of the fact that relay Br is still operated. However,depending upon the relation between A and B, i.e. the first remaining Adocument and the last B document, the former should follow the samedirection as the latter or not. It is clear that when A B, A shouldfollow the same direction as B, and when B A, A must follow thedirection opposite to that taken by B in order to start a new outputsequence with the first remaining A document. Yet, it is only when onehad C A B, that the comparator would still indicate a reversal of outputwhich in the particular case of the first remaining document for batchsorting, is wrong. Likewise, if the condition which caused thecomparator to dispatch the last B document was B C A, this did notindicate a change of output for the last B document and correspondinglyit does not indicate a change of output for the first remaining Adocument, which latter indication is wrong since it is in thisparticular case that the first remaining A document should follow thedirection opposite to that taken by the last B document.

A very simple solution to the dispatch of the first remaining A documentto the correct output position can be found if the comparator circuit CPis arranged in such a way that when it detects the particular conditionwhich means a change of output direction to start a new sequence withthe lowest of A or B, after this indication has been received andutilised, the comparator circuit C? will automatically be reset to therespective conditions.

This means that the relation between A and B is maintained as receivedbut the relations between A and C on the one hand and B and C on theother hand, are both artificially reversed.

Accordingly, out of the three possible conditions which were mentionedabove as those which are the only ones which might have caused thedeparture of the last B document, there remain only two, i.e.

since the third was automatically and artificially changed into thefirst of the two above.

If, as already mentioned, the opening of change over contact bd, uponthe operation of Bdr, changes the condition B C of the comparator, intoC B, the two possible conditions will then become A C B and C B Arespectively. It is clear that these last two conditions respectivelyindicate that A should be sent forward in the same direction as B, orthat A should be sent forward in the direction opposite to that taken byB. (One should recall that C is always used to indicate the previousdocument which was dispatched to the points and which in these cases wasthe last B document.)

The above explained modifications in the state of the comparatorconsequent upon the operation of relay Bdr would however remain withouteffect as far as the activation of the output terminals P P P and P ofthe comparator circuit CP (FIG. 2) are concerned, since it will berecalled that the comparisons are made active upon the authorizingpulses at terminal P being ter minated. Hence, despite the forced changeon the comparator state due to the opening of contact bd terminal P willremain activated and consequently relay Br would stay energised. Thiswould be of no consequence in view of the closure of contact bd whichwill anyhow produce the departure of the first remaining A document, butif terminal P was activated when the last B document was sent throughthe points, and if B A, the activation of this last terminal should nowbe replaced by the activation of terminal P to permit the firstremaining A document to be moved to the output position opposite to thatto which the last B document was directed. The missing trailing edge ofthe authorizing pulse normally appearing at terminal P will be replacedby a pulse generated by the closure of the connection between terminalsP and P;,, which pulse will exploit the modified state of the comparatorcircuit CP. Hence, depending on whether A E, terminals P will remainactivated or not, the deactivation of this terminal resulting of coursein the activation of terminal P In fact, the only two possibleconditions which are attained upon the operation of relay Bdr willalways cause the deactivation of terminal P causing the release of relayBr, while relay Ar will now be energised as a result of the activationof terminal P Therefore, the first remaining A document will be directedto one of the two output positions depending on its value, and thefurther remaining A documents will be successively sent to the pointsposition H to be directed to one of the two output positions, a changein the output position being obtained every time that a sequence of remaining A documents ends. Hence, the remaining A documents will bedistributed to the two output positions in accordance with their inputsequences, and the principle of distributing the documents to the twooutput positions depending on the available sequences will bemaintained.

Although it has been shown that relay Ar will in any case be operatedfor the first remaining A document, the closure of make contact bd willnevertheless play its part during the dispatch of further A documents.Since, as mentioned above, the comparator is forced by the opening ofthe connection between terminals P and P into a condition correspondingto C B, from then on the only three possible conditions which can beimpressed on the comparator are For the first and the last conditionsabove, these will cause the A document to be dispatched, with a reverseof the output position for the last condition. For the second conditionhowever, this corresponds to a B document being sent in the oppositeoutput position than the one previously followed by the previousdocument and hence, it is in such a case that make contact bd will stillpermit the A document in the intermediate position A to be dispatched,in a direction opposite to that followed by the previous A document.

When the last of the remaining A documents is advanced to theintermediate position A, contact ka will be closed as a result of the Ainput position and store having also been emptied and upon the operationof the relay .Aar, relay Adr will energise in the same manner as relayBa'r was previously operated. Upon relays Bdr and Adr being bothenergised, relay Fr operates through a circuit including contacts ad,and but, in series. it interrupts the holding circuits for these tworelays at make contact f Relays Adr and Bdr consequently release and inturn cause the release of relay Fr. The latter should be made slow torelease in order to ensure that both re lays Aa'r and Bdr are releasedbefore relay Fr can again close its contact f Upon the points position Hhaving been liberated by the last A document, the circuit will becompletely released.

During a sorting pass it might be desirable for some reason to stop thesorting operation. Either one may wish to stop the operations and make acompletely new sorting pass or else, a temporary hold in the operationis desired, it being intended to restart the latter at a later moment.

When a final stop is desired, contact kt will be temporarily closed by asuitable push-button arrangement resulting in the operation of relay Trthrough break contact .9 of the starting relay which should of course bereleased at that moment, and break contact ku Relay Tr in operating,prepares, via make contact 1;, an operating circuit for relay Er. Thelatter will be completed upon either relay Aar or relay Bar beingoperated to indicate that a document has reached an intermediateposition and should now be dispatched to the points position. Forinstance upon relay Aur being energised, the closure of make contact aawill energise relay Er. This relay locks through its make contact e inseries with the break contacts hb and s0 At make contact e,, theoperating circuits for various relays will be interrupted, and inparticular, relay Acr will be prevented from operating upon the Adocument having caused the operation of relay Aar having been dispatchedto the points position. Hence, no further A document will be transferredto the intermediate position A. The sorting pass will be ended becausethe comparator is now in such a condition that relay Ar is energised andaccordingly since relay Br is dc-energised, the B document in thecorresponding intermediate posi tion stays put and blocks also furtheradvance of documents, this time for the B input position. Relay Er willbe released upon the temporary operation of relay I-Ibr subsequent tothe points having been returned to their normal position upon the last Adocument having been dispatched to one of the two output positions. Thesorting pass is definitely ended, all relays being released with theexception of relay Ar.

Another result of the operation of relay Er will have been theinterruption of the connection between terminal P and the 0 input of BS(FIG. 2) due to the opening of contact e This will cause BS, to beplaced in its 0 condition in a manner previously explained, with theresult that the local advance pulses at terminal P will wipe out thenumbers inscribed in SRA and SRB.

If an intermediate stop is desired, the operations will be similar tothose which have just been described, except that the operation of relayEr will be initiated due to the closure of contact ku, controlled by asuitable key or push-button. In such a case, however, relay Tr will notbe operated. Instead, relay Ur will be operated through break contacts sand kt, and make contact ku It locks through contacts u, and sb inseries with either a or b Hence, despite the opening of contact a theconnection between terminal P and the 0 input of BS will be maintainedthrough make contact n to prevent wiping out the registers SRA and SRB.Since relay Ar and consequent ly relay Ur remain operated during theintermediate stop, when the sorting pass is restarted by the closure ofcontact ks, the displacement of contact 5, cannot interrupt theconnection between terminal P and the 0 input of BS Hence, in thisparticular case, the registers SRA and SRB will not be wiped out at thebeginning of the operations so that the previous numbers stored in theseregisters will be used in order to decide whether the document whichremained in the intermediate B position, or the new A document sent tothe corresponding intermediate position, should be sent forward to thepoints position and thence to one of the two output positions. Uponrelay Sbr having been operated, which means that at that time relay Srhas already released, the holding circuit for relay Ur will beinterrupted at contact sb; and this relay will release without anypossibility of the connection between terminal P and the 0 input of BSbeing interrupted. Relay Ur should be assumed to be slow releasing sothat it remains operated if relay Ar releases to be replaced by theenergisation of relay Br, or vice-versa.

The control of the sequences of operations having been fully described,the comparator circuit CP represented as a block in FIG. 2 will now bedetailed by referring to FIG. 5.

The comparator circuit CP of FIG. 5 is shown to include three comparatorunits CPA, CPR and CPC each provided with four input terminals such asPic, P P and P for CPC and with two output terminals such as P and P forthis same comparator unit. All three comparator units are absolutelyidentical and CPC is detailed in FIG. 6.

-As shown in FIG. 6, each comparator unit comprises a bistable device, amonostable device, 6 gates and 2 inverters. Terminal P which as shown byFIG. 5 is connected to terminal P,, which as shown by FIG. 2 receivesthe clock pulses from the document which is being read, constitutes oneinput of the coincidence gate G whose other input is activated when thebistable device BS is in its 1 condition. This will be obtained upon apulse appearing at the 1 input of B8 which is connected to terminal P Inturn, this terminal is connected to terminal P (FIGS. 2 and 5), and atthis terminal will appear a pulse either corresponding to the leading orto the trailing edge of the authorizing pulse which appears at terminalP when a document is being read. It will be assumed that only theleading edge of this authorizing pulse can be eflective to trigger BSinto its 1 condition. From that moment, every clock pulse will be ableto pass through the gate G and will trigger the monostable device MS;into its oil normal condition where it will remain for a period of 60microseconds. When M8 returns to its condition, a trigger pulse whichwill be termed a comparison pulse, will be generated at its output. Thisis indicated in FIG. 6 by condenser coupling from the 0 output of MS; toindicate that the condition is only a transient one when M flops back toits normal condition. Hence, M8 functions as a delay device and thecomparison pulses derived from its output as clock pulses are applied toits input are shown in FIG. 4. These pulses are applied to inputs of thecoincidence gates G and G the outputs of which respectively constituteone input of the coincidence gates G and G whose outputs arerespectively connected to terminals P and P The other input of G isconnected to terminal P while the other input of G is connected toterminal P Further, terminal P is connected to the input of the inverterI whose output constitutes the second input of G On the other hand,terminal P is connected to the input of the inverter I whose outputconstitutes the second input of G Finally, terminals P and P act asinputs for the mixer gate G whose output is connected to the 0 input ofBS As shown by FIGS. 5 and 2, terminal P is connected to stage 1 of SRAthrough terminal P On the other hand, terminal P is connected to stage Iof SRB through terminal P This means that the electrical conditionsappearing at terminal P and P correspond to the digits which are at thattime inscribed in stages I of SRA and SRB respectively.

With shift registers of n+2 stages, where n is the number of binarydigits necessary to characterise a number, as shown by FIG. 2, aneventual information pulse always precedes the corresponding clock pulseby 100 microseconds as shown in FIG. 4. Hence, with a previous number Cstored in SRA on the stages 1 to n included, when a new number A beginsto be read, the eventual first information pulse will be registered instage 0 of SRA. In other words, if each stage of the registers is mainlyconstituted by a cold cathode tube, the presence of this firstinformation pulse characterising the binary digit 1 will ionize thiscold cathode tube. On the other hand, if there is no information pulse,corresponding to the binary digit 0, stage 0 of SRA will not be ionized.A hundred microseconds afterwards, the first clock pulse will advancethe pattern recorded on SRA and SRB by one stage. This means that thepreviously recorded numbers C and B will now be registered on stages 2to n+1 included of SRA and SRB respectively while the first digit of thenew number A will be recorded on stage i. Since the first clock pulseappearing at terminal P (FIG. 6) is allowed to produce a comparisonpulse microseconds afterwards and which is applied to the gates G and Gthis comparison pulse will be able to compare the conditions existing atterminals P and P Whereas the condition at terminal P corresponds now tothe first binary digit of number A, the electrical condition at terminalP corresponds to the first binary digit of the number B previouslyrecorded in SRB, and which is allowed to recirculate in that register.

If it is assumed that a 0 digit in stage 1 of SRA or SRB corresponds toan activating potential at terminals such as P or P the correspondinggate G or G will be made conductive to pass the comparison pulsesderived from the clock pulse. Since the gates G and G are respectivelycontrolled from terminals P and P through the inverters I and 1,, a 0digit will block the corresponding gate G or G while a 1 digit will makethe corresponding gate G or G conductive to accept the comparison pulse.This means that if the first binary digits of A and B are both 0 or bothI, the comparison pulse will be blocked either by the gates O and G orby the gates G and G If the first binary digit of A is 0 while the firstbinary digit of B is l, gates G and G are conductive while gates G and Gare blocked. Hence the comparison pulse will be able to how through thegates G and G in series to appear at terminal P On the other hand, ifthe first binary digit of A is 1 while the first binary digit of B is 0,the comparison pulse will appear at terminal P80.

As soon as a pulse appears either at terminal P or P while the number Ais progressively inserted into SRA while at the same time the previouslyrecorded B number in SRB is circulated through the stages 1 to n of thisshift register, this comparison pulse will pass through G to trigger BSinto its 0 condition. This blocks gate G which means that the next clockpulse appearing at terminal P will not be able to generate acorresponding comparison pulse.

The reason for this blocking action as soon as a comparison pulseappears either at terminal P or P is that it has been assumed that thebinary digits used to characterize the numbers have been ordered so thatthe first binary digit of any number has the greatest weight, while thelast has the smallest weight, and in general the weight of any binarydigit is smaller than that of the previous digit and larger than that ofa next digit. Hence, as soon as it has been detected that a binary digitof number A is greater or smaller than the binary digit of same weight,of the B number, one knows that A is greater or smaller than B. Further,the comparison between the two numbers must cease to be etfective sinceotherwise it is obvious that a wrong result might be obtained.

The above docs not essentially mean that the numbers should beregistered as binary numbers. They are merely recorded by way of nbinary digits in any suitable manner but such that when all the numbersare ordered, all the respective binary numbers corresponding to thecoded representation of the numbers are in the same order. For example,numbers of 11/4 decimal digits could be recorded by n binary digitsusing 4 binary digits to characterise a decimal digit. The first 4binary digits would correspond to the decimal digit of highest weight ofthe decimal number and so on. Further, for every combination of 4 binarydigits characterising a decimal digit, the first binary digit would havethe highest weight and so on. For example, the following code could beused to characterise the decimal digits:

From this coding scheme it is seen that the first binary digit has aconstant Weight of 5, the second a weight of 3, the third a weight of 2and the fourth a weight of 1. According to the rank of the decimal digitconcerned,

these weights will then be multiplied by corresponding powers of 10.Although this binary coding of the decimal digits uses a so-calledconstant weight code, this is not essential.

It may be remarked also that although the circuit FIG. 6 is concernedwith the case where the highest weights appear first, exactly thereverse order could be used with the lowest weight in front. In such acase however, the gate G should be suppressed and it would be the lastcomparison pulse appearing either at terminal P or P which woulddetermine which of the two numbers is greater that the other. Since asshown by FIG. 5, terminals P and P lead to the respective inputs of atwo input bistable device BS the latter might be switched over from oneto the other stable condition several times during the dynamiccomparison of the two numbers. However, only the last pulse appearing atone of the two terminals would determine the correct result of thecomparison. Hence, provided the state of BS is not exploited before allthe digits of the two numbers have been compared to one another, thescheme shown in FIG. 6 could also be used when the binary digit with thelowest weight is in front.

One will remark also that the arrangement of FIG. 6 does not necessitatethe comparisons between pulses of substantially the same length. Theconditions at terminals P and P will remain for about 170 microsecondsand the comparison pulse at the inputs of G and G is a trigger pulse ofvery short duration.

The shift registers SRA and SRB shown in FIG. 2 are shown to be providedwith an (n+2)th stage called the stage, at the input. These extra stagesare not absolutely essential and might be dispensed with if the clockpulses instead of lagging by a half period of 100 microseconds behindthe eventual corresponding information pulses, would lead these pulsesby the same interval of time. What is essential is to have at least n+1stages for the registers so that a digit of the incoming number such asA can always be compared with the digit of corresponding rank of thenumber recirculating in B, or of the number C leaving SRA.

Returning to FIG. 5, the comparator units CPR and CPA function inexactly the same way as the comparator unit CPC detailed above inrelation to FIG. 6. From FIGS. 5 and 2 it will be seen that whereas CPCsucces sively compares the digits A and B, CPB compares the digits of Aand C and still assuming that A is the number which is beingprogressively registered in SRA, CPA will be ineffective at that momentin the sense that it will merely compare the number B with itself sincethe number B is recirculating through SRB as shown in FIG. 2. If thenumber B was coming into SRB while the number A previously recorded inSRA was recirculating through that register, it would be the comparatorunit CPB which would not make a comparison beyond comparing A withitself.

Hence, taking as example the case of A being inserted in SRA, A iscompared with B and A is compared with C the outgoing number. Despitethe fact that B is not compared with C, the two comparisons which areperformed will nevertheless provide an indication of the order betweenA, B and C which can be ordered in six different ways, without regard tothe special cases of equalities.

The reason justifying the fact that the recirculating number B is notactually compared with the outgoing number C is the following:

If when A comes in to replace C in SRA, the bistable device BS,indicates B greater or smaller than C, these relations are respectivelyapplicable with respect to the C number presently leaving SRA despitethe fact that they were obtained with regard to the number which leftSRB when the B number now inscribed in SRB was inserted therein.

The bistable device BS is of course analogous to the bistable device88;, and records the results of the comparison given by CPA by havingits two inputs connected to the terminal P and P through the mixer gatesG and G respectively. Likewise, BS indicating the relation between A andC has its two inputs connected to the terminal P and P through therespective mixer gates G and G If it is assumed, BS registers B C, itmeans that when B came into SRB it was found larger than the numberwhich left SRB at that time. If the B number has stayed into SBR sincethen, it must mean that the number which was at that moment stored inSRA left and that it was therefore smaller than B, and greater than thenumber which left. Since then, all the numbers which have passed throughSRA cannot have decreased in value but they must have remained smallerthan B. Hence, the number C which is new leaving SRA must in fact besmaller than B.

On the other hand, if BS indicates C B, it means than when B came intoSRB it was smaller than the number leaving SRB at that time. If B stayedin SRB, this must mean that the number which was at that time stored inSRA left and that it was therefore greater than the number which leftand than B, provided that the number which left and was replaced by Bwas not at the same time also greater than the number stored in SRA.With this important provision on which a further explanation will begiven, the number which left SRA after B had been registered in SRB musthave been greater than B. Further, the numbers which have since thenpassed through SRA cannot have decreased in value and the number C whichis now leaving SRA to be replaced by A must therefore be greater than Bas indicated by the condition of BS Hence, the above reasoning provesthat the condition of B8 i.e. B greater or smaller than C does give acorrect indication of the relation between the number C presentlyleaving SRA and the number B stored in SRB and recirculating in thelatter register, despite the fact that B8, was set in its conditionwhile the B number was compared with a number other than that presentlyleaving SRA. But, this reasoning is only valid provided an outgoingnumber was not at any time greater than the incoming number and greaterthan the recirculating number. Such a condition can of course, arise,but the comparator is provided with means which will cause an automaticrestoration of the bistable devices BS; and BS, upon these being foundto respectively indicate C B and C A. If such an condition arises, BSand B5, are automatically placed in the conditions B C and A Crespectively. This automatic reset was already mentioned previously andas particularly useful in connection with batch sorting upon theoperation of relay Adr or Bdr. The main usefulness of this automaticrcset is however to permit making only a comparison between the incomingand the outgoing number, and between the incoming and the recirculatingnumber, while avoiding making a comparison between the recirculating andthe outgoing number. This could, of course, be made but it would meanthat the comparator units CPA and CPB would not have permanent inputconnections. Upon a number coming into SRA, the connection betweenterminals P and P would have to be replaced by a connection betweenterminals P and P On the other hand, upon a number coming into SRB, theconnection between terminals P and P would have to be replaced by aconnection between terminals P and P This would then permit to makeeffective comparisons between the three pairs of numbers. This is notdifficult to achieve since the switching over could be controlled by theactivating potential present either at terminal P or at terminal P andwhich indicates the shift register into which a number is coming, butadditional gating means would be necessary.

One may remark that the reasoning justifying the comparison of two pairsof numbers only out of the three is incomplete in so f .r as thecondition B C is concerned since this might have resulted from theexplained automatic reset, upon the B number in SRB and a numberentering SRA having both been found smaller than the number which wasleaving SRA at that time. But, if the B number stayed since then in SRB,this must mean that the number having entered SRA at that moment wassmaller than B. One is therefore brought back to the general reasoningfor the condition B C since although all the numbers having passedthrough SRA may have increased in value, they must nevertheless haveremained smaller than B. Hence the C number-which is now leaving SRA istruly smaller than B as indicated by the condition of BS After a numberA has been fully entered in SRA, the bistable devices BS BS BS are nowset in respective conditions which indicate the correct relationshipbetween A, B and C. The circuit of FIG. 5 is therefore ready to exploitthese conditions in order to activate one of the terminals P and P andone of the terminals P and P This activation will be performed by thedifferentiated trailing edge of the authorizing pulse at terminal P andwhich appears at terminal P Whereas the leading edge of this authorizingpulse was used to make the circuit of FIG. 6 ready to make a comparison,the inverter 1;, indicates that the differentiated trailing edge of thisauthorizing pulse will appear as an active signal at the output of 1,,which is connected to an input of the mixer gate G As the output of G isconnected to an input of the three gates G G and G this output signalwill attempt to pass through one of these three coincidence gates. Thefirst G has two further inputs respectively controlled by ES; indicatingC B and by BS indicating C A. The second, G has two further inputsrespectively controlled by BS indicating C B and through the mixer gateG and by BS indicating A C. Finally, the third, G has two further inputsrespectively controlled by ES, indicating B C and by BS indicating C A,through the mixer gate G Further, alternatively to G being controlled by138., indicating C B it can also be controlled by BS indicating B Athrough G Similarly, G apart from being controlled by BS indicating C A,it can also be controlled by BS indicating A B through G It can beremarked that when a pulse appears at the output of G one and only oneof the three coincidence gates G G and G will always be ready to letthat pulse flow through.

. If the pulse is able to flow through gate G this means that theconditions are such that the A number corresponds with a document whichshould be made to advance to the points position and to be directed toan output position which is the same as the one to which the C documentwas sent. Also this will mean that the next A document should come fromthe A input position to have its number inscribed in SRA. Hence, theoutput of G constitutes the first input of the bistable device BS, andthe output terminal P corresponding to the A condition of BS will beactivated. Likewise, if it is G which delivers an output signal, thiswill trigger BS into its B position if it was not already in thatcondition and terminal P will be activated.

If the pulse at the output of G is on the other hand able to penetratethrough G this is because A and B are both smaller than C. Hence, achange of output is required either for the A or the B document. Theappearance of this pulse at the output of G does not therefore indicatewhich of the A or B document should be sent forward, but that whateverdocument is sent forward, it will have to follow a direction opposite tothat taken by the C document. This output pulse is applied to the singleinput of the bistable device BS which therefore acts as a scale-of-twocounter. If it was in condition C activating terminal P it will now passinto condition D activating terminal P and vice versa.

Apart from being connected to the single input of BS the output of G isalso connected to the inputs of the monostable devices M5 and M3 Thefirst is shown to have a time constant of 50 microseconds and the seconda time constant of microseconds. They serve as pulse delay devices forthe pulse which may appear at the output of G Some 50 microseconds afterhaving been triggered by the pulse at the output of G M5 by beingrestored to its stable condition, will produce a pulse which. throughthe respective mixer gates G and G will trigger B5,, and BS intoconditions respectively indicating B C and A C. This is the resetoperation previously explained.

A further 50 microseconds afterwards, M5 which was triggeredsimultaneously with M5 by automatically returning to its stable 0condition, will generate a pulse which through G will be applied to thethree gates G G and G just as the pulse at the output of 1;; was appliedto these three coincidence gates. However, G is now blocked and either Gor G is unblocked. Hence, the pulse produced by MS, will appear eitherat the output of G or at the output of G to place or leave BS-; in thecondition indicating whether the A or the B document should be sent tothe points position.

The time constants of M5 and M8 are not in any way critical since it ismerely desired that an output pulse generated by M8 should follow itsinput pulse and that the output pulse generated by MS, should followthat generated by M8 One could, of course, trigger MS; with the outputsignal of M8 and in such a case M8 and M8 might for example have thesame time constant of S0 microseconds.

A further input of the mixer gate G is connected to terminal P which asshown by FIGS. 3 and 2 can receive a pulse when either of the batchsorting relays Adr or Bdr operates to connect terminal P through makecontact ad or bd to terminal P via a differentiating circuit indicatedby a condenser coupling. Hence, this pulse which is needed due to thelast document in an input position not having been replaced by a furtherdocument, will simply investigate the conditions of the comparatorcircuit CP in exactly the same way as the pulse generated by thetrailing edge of the authorizing pulse at terminal P investigates theconditions of the comparator after every comparison. Such a pulse forbatch sorting will of course have been preceded by the opening of theconnection between terminals P and P or P and P having, through themixer gates G or G caused B5,; or BS to be placed in the conditions C Bor C A respectively.

With respect to the pulse generated by the closure of relay Adr or Bdrat terminal P the design of the comparator circuit CP including thereset feature has the further advantage that eventual contact vibrationscan easily be dealt with. Indeed, if more than one effective pulseshould appear at terminal P and if BS and BS indicate C B and C A, morethan one pulse could reach the scale-of-two circuit BS which mighttherefore respond incorrectly. However, some 50 microseconds after thefirst pulse, M8 will trigger BS and 138;, so that G becomes blocked andthis gate cannot accept eventual further pulses at the terminal P Gate Gor G can accept them together with the pulse generated by MS, but thisis of no consequence since gates G and G feed into a particular input ofthe two input bistable devices BS The time constant of MS; can evidentlybe selected so that G cannot pass more than one pulse appearing atterminal P It will be observed that the circuit of FIG. 5 does not needto exploit an eventual condition of the comparator units CPA, CPB andCPC such that one of these would indicate that the two numbers which ithas compared are equal. Considering the circuit of FIG. 6. thecomparator unit can readily provide such an indication by the fact thatBS, after a comparison, would have remained in its 1 condition. However,as will be now explained, the detection of such an equality condition isnot needed. This means that, if the numbers are compared with theweights of their digits in ascending order, lowest weight in front, notonly the gate G but also the bistable device BS could be dispensed with.In such a case, one might also avoid the gate G Further, the monostabledevice MS, which is provided in each comparator unit such as CPC couldthen be common for the three comparator units since an individualblocking of the comparison pulses arriving at a particular comparatorunit such as CPC would no longer be needed. One would merely requirethat the comparison pulses follow the clock pulses by some suitableinterval of time necessitating only a single common monostable device.

The adequate functioning of the circuit of FIG. 5 in the case ofequalities between numbers, is again due to the reset feature for thebistable devices BS, and BS in the event that both A and B are smallerthan C.

Two cases of equalities can be considered. Either the incoming number inone register is equal to the number which is already stored in the otherregister, or it is equal to the number which it replaces in said oneregister.

Considering the case of the numbers A and B having been compared withthe outgoing number C with the result that A went out, one will firstassume that the number A which comes in to replace A is equal to B. If Awent out, this means that one had the conditions Considering now that Ais equal to B, the three previous conditions will respectively lead toThese last three conditions can be readily verified by considering forexample the first. Since one had B A, this will on the one hand lead toB A since the comparator unit CPC and more particularly BS will stay inits previous condition. On the other hand, the previous B A conditionleads to A' A since B=A'.

As can be readily inspected, the three possible conditions obtainedafter the insertion of A'=B into SRA are such that either the A or the Bdocument is sent forward which is immaterial, but that the B documentwill be sent in the reverse direction to that taken by the A document inthe case that A was greater than C which was in turn greater than B.

In fact, the three conditions which have been considered above includethe one where C is greater than B which in turn is greater than A, whichcondition cannot stay when the reset is used. The automatic reset willproduce instead B greater than A which in turn is greater than C. Hence,with or without automatic reset, the case of an incoming number beingequal to the number already stored in the other register is adequatelydealt with despite the absence of the inspection of an equality in theactual comparison.

Considering now the case where A=A, the three possible conditions whichmay have led to the entrance of A to replace A are the same as beforebut in view of 28 the equality A'=A one can now derive the correspondingconditions This can be explained for example by considering the previousB A C condition, i.e. the first possibility. On the one hand, A C leadsto A' A since the comparator unit CPB and particularly BS will stay inits previous condition. 0n the other hand, B A leads to B A in view ofthe equality between A A'.

For the first two possibilities, one observes that the A document shallnecessarily follow the A document in the same direction, which is thecorrect course. For the third possibility, this indicates that the Bdocument shall follow the A document. This is not correct because itwould mean that despite A'=A, the A document is not allowed to followthe A document although it is smaller than B but not smaller than A.

However, this third possibility arises when both A and B are smallerthan C which condition is not allowed to persist until the nextcomparison due to the automatic reset. Hence, the third possibility willin fact not exist and it is automatically replaced by the first whichleads to correct operations.

Although the invention has been described in relation to the sorting ofdocuments such as cheques bearing magnetic marks indicating theircharacteristic numbers, or being supported on document carriers which inturn also carry pieces of magnetic tape on which said numbers areinscribed, it will be clear that the invention is not particularlylimited to such an application. First of all, if one considers documentcarriers, the documents might well be ordinary letters for example,which would be automatically sorted in the manner explained after themail had first been processed by operators to associate each letter withits carrier bearing indicia characterising the address of thecorresponding letter. Further, there might not be any documents at allassociated with the numbers. This might for example correspond totelephone numbers associated with satellite information characterizingthe cost of a telephone call made by the corresponding telephonesubscribers. Such information may be randomly recorded as the calls aremade, but later on a sorting in accordance with the calling substationnumbers is useful for accounting purposes so that any calling subscribercan be properly debited for all his calls. In such a case, there wouldbe two input magnetic tapes and two output magnetic tapes and eachsorting pass would be made substantially in the manner described, thesequence controller of FIG. 3 being of course suitably modified, but thecomparator arrangement of FIGS. 2. S and 6 remaining substantially thesame.

Each number which is used for sorting into the required final naturalorder will in general be accompanied by a satellite number or numbers.In the case of cheque sorting which has been particularly envisaged. thesorting is made in accordance with the account number but the latter isalso accompanied by a number characterizing the amount. The two numbersmay be serially inscribed on the same piece of magnetic tape or not. Inthe description of the embodiment of the invention, no particularattention was paid to the account number being followed or not by theamount. If it is, the shift registers can Well store the two numbers inseries and in such a case the sorting will be made in accordance withthe account numbers as recorded, but for cheques bearing the sameaccount numbers, a subsidiary sort will automatically be made inaccordance with the various amounts of these cheques. This may in factprove to be a useful feature. Alternatively, a separate piece ofmagnetic tape could be used for recording the amounts,-

or in general arrangements could be made so that the amounts or moregenerally any satellite information would not be read at all, in whichcase the shift registers would only need to record the account numbers.Then, for a series of cheques bearing the same account numher, after thefinal sorting pass, these would be found together but they would notnecessarily be ordered in accordance with the amounts.

The use of the shift registers in accordance with the invention does notnecessarily imply the use of the particular comparator circuit shown inFIG. 5, but the latter has been shown to possess advantages particularlyfrom the point of view of simplicity. Also, the shift registers areinitially made to indicate numbers in order to properly start a sortingpass. Again, this is not absolutely essential since one could also makea correct start by a special use of the comparator circuit at the startof the operations, while at least one of the arbitrary fictitiousnumbers would still be stored in the shift registers. Such a solution ishowever believed to be rather more complicated than the simple wipingout of the shift registers at the start of the operations.

Further, the gates such as 6,, G and G G might not be found absolutelyessential bearing in mind that pulses either appear at P and P or at Pand P and that it is only required that the eventual information pulsesat P or P should be directed to the 0 stage of either SRA or SRBrespectively, which is in any case obtained by G, and G Therefore, whilethe principles of the invention have been described above in connectionwith specific apparatus, it is to be clearly understood that thisdescription is made only by way of example and not as a limitation onthe scope of the invention.

What is claimed is:

1. In an electrical sorting system for sorting electrically representednumbers associated with electrically represented satellite informationin which the numbers to be sorted are arranged in first and secondinitial successions of N1 and N2 numbers, each succession being in anyarbitrary order, and the sorting is done by a binary collation processwhich obtains a new pair of successions of the N1 and N2 numbers in sucha manner that the first sequences of numbers ordered in the desiredmanner and found in said two initial successions are merged together toconstitute the first sequence of the first new succession, and thesecond sequences found in said two initial successions are also mergedtogether to constitute the first sequence of the second new succession,and similar merging operations produce a new sequence alternately forthe first and the second new successions, the combination of a first anda second electrical shift register, each having at least n+1 stages,where n is the number of binary digits needed to characterize anynumber, means for progressively inserting numbers alternatively in saidfirst and second registers respectively from said first and said secondinitial successions, means for simultaneously and progressivelyrecirculating a number in one of said registers while a new number isbeing inserted in the other of said registers, means responsive to theprogressive insertion into one of said registers of a number from one ofsaid initial successions for progressively expelling the numberpreviously recorded therein, first comparing means for comparing theexpelled number from said first shift register digit-by-digit with thenumber progressively inserted therein, second comparing means alsoresponsive to the progressive insertion of a number into one of saidregisters from one of said initial successions for comparing saidinserted number digit-by-digit with the number being recirculated insaid other register, third comparing means responsive to the progressiveinsertion into said second register of a number from said second initialsuccession for comparing the number being expolled from said secondregister digit-by-digit with the number being inserted therein, meansresponsive to the complete insertion of a number from one of saidinitial successions into one of said registers and controlled by all ofsaid comparing means for indicating the order of the three numberscompared, and means controlled by said indicating means for operatingsaid number inserting means to insert a number from that successioncorresponding to the register from which a number is to be expelled.

2. In an electrical sorting system, the combination, as defined in claim1, in which the indicating means comprises first, second, and thirdbistable devices controlled respectively by the first, second and thirdcomparing means, means for triggering each of said bistable devices intoone state when a particular one of the two numbers compared by thecorresponding comparing means is larger and into the other state whenthe other number is larger, first, second, and third gates, means forcausing said first gate to deliver an output signal when said first andthird bistable devices together indicate that the number expelled fromeither register is larger than the number in both registers, thusindicating that the expelled number is the last number of a sequence ina first or second new succession, means for causing said second gate todeliver an output signal when said first and third bistable devicestogether indicate that said expelled number is smaller than the numberin said first register and larger than the number in said secondregister, thus indicating that a sequence in a new succession is notcomplete and that the sequence should be continued from said firstregister, means for causing said third gate to deliver an output signalwhen said first and third bistable devices together indicate that saidexpelled number is smaller than the number in said second register andlarger than the number in said first register, thus indicating that asequence in a new succession is not complete and that the sequenceshould be continued from said second register, a fourth bistable deviceoperating as a scale-of-two counter, the two stable states of whichcorrespond respectively to said first and second new successions, meansfor causing signals delivered by said first gate to trigger said fourthbistable device alternately from one bistable state to the other, afifth bistable device in which the first and second bistable statescorrespond respectively to said first or said second register having tocontinue the sequence including said expelled number, means for causingthe signal delivered by said second gate to trigger said fifth bistabledevice into its first state and means for causing the signal deliveredby said third gate to trigger said fifth bistable device into its secondstate.

3. In an electrical sorting system, the combination as defined in claim2, further comprising means responsive to the signal delivered by thefirst gate for causing a reversal of the states of both the first andthird bistable devices, and means for preventing the second and thirdgates from delivering a signal until after said reversal has beenaccomplished.

4. In an electrical sorting system, the combination, as defined in claim2, further comprising means responsive to one of the initial successionsof numbers having all been inserted in the corresponding register forrearranging the states of the first and third bistable devices to causethe first gate to deliver an output signal, whereby any remainingnumbers are alternatively stored in one or the other of the two newsuccessions in accordance with their initial sequences.

References Cited in the file of this patent UNITED STATES PATENTS2,735,082 Goldberg et a1. Feb. 14, 1956 2,785,856 Hobbs Mar. 19, 19572,798,216 Goldberg et a1 July 2., 1957 2,865,567 Booth Dec. 23, 1958

